The present invention is related to gas turbine engines, and in particular to variable rotor blades and variable rotor blade actuation mechanisms.
Gas turbine engines operate by combusting fuel in compressed air to create heated gases with increased pressure and density. The heated gases are ultimately forced through an exhaust nozzle, which is used to step up the velocity of the exiting gases and in-turn produce thrust for driving an aircraft. In turbofan engines the heated gases are used to drive a turbine for rotating a fan to produce thrust, and to drive a turbine for driving a compressor that provides the compressed air used during combustion. The compressor section of a gas turbine engine typically comprises a series of rotor blade and stator vane stages. At each stage, rotating blades push air past the stationary vanes. Each rotor/stator stage increases the pressure and density of the air. Stators convert the kinetic energy of the air into pressure, and they redirect the trajectory of the air coming off the rotors for flow into the next compressor stage.
The speed range of an aircraft powered by a gas turbine engine is directly related to the level of air pressure generated in the compressor section. For different aircraft speeds, the velocity of the airflow through the gas turbine engine varies. Thus, the incidence of the air onto rotor blades of subsequent compressor stages differs at different aircraft speeds. Gas turbine efficiency is, therefore, closely linked to the ability of a gas turbine engine to efficiently direct air flow within the compressor section.
One way of achieving more efficient performance of the gas turbine engine over the entire speed range, especially at high speed/high pressure ranges, is to vary the pitch of the vanes to optimize the incidence of the airflow onto subsequent compressor stage blades. Conventional variable pitch compressor sections rely on variable stator vanes, as it is typically more feasible to include complex actuation mechanisms for stationary parts. Stator vanes are typically circumferentially arranged between stationary outer and inner diameter shrouds, which permits them to rotate about trunnion posts at their innermost and outermost ends to vary the pitch. Rotor blades, however, are only supported at their innermost end by the rotor disk, as the blade must rotate with the turbine shaft during operation of the engine. Thus, attempts at variable pitch compressor sections have typically been limited to variable stator vanes due to the complexity necessary for actuating a rotating blade, and to the heavy centrifugal loads placed on the blades during engine operation.
Another way of achieving more efficient compressor flow is to include variable camber blades and vanes. Blades and vanes comprise arcuate shaped bodies extending between a leading edge and a trailing edge. The amount of curvature of the body, or camber, affects the speed and trajectory of the air. Thus, variable camber blades provide an additional means for optimizing engine efficiency. However, due to the complexity of varying the shape of a body that must remain rigid under high stress while rotating, variable camber compressor sections have typically been impractical.
Thus, there is a need for variable pitch and variable camber rotor blades for gas turbine engines.